Traveling wave tubes



Jall- 26, 1960 G. coNvERT TRAVELING WAVE TUBES Filed Feb. 25, 1954 l f 1 l f I f 1 f f 1 l l f 1 1 l l l l l 1 1 l 1 u .15.,

mfman/ INVENTOR CONVERT A OR nited .States Patent"t 2,922,920 TRAVELING WAVE TUBES Guy Convert, Paris, France, assignor to Compagnie Generale de Telegraphie Sans Fil, a corporation of France The present invention relates to an improvement to a tube described in the U.S. Patent No. 2,580,007. This patent discloses a traveling wave amplifier tube in which the output energy is collected both from the ultra high frequency wave propagating along the delay line of the tube and from the electron beam, propagated along this line, through the medium of a cavity Vresonator through which the beam is shot. As is known, in the course of its propagation along the delay line, the beam yields energy to the ultra high frequency wave to amplify the latter and, simultaneously, is modulated by this wave.

It has appeared that it is sometimes dicult to combine the energy Vabstracted from' the ultra high frequency wave with the energy provided by the electron beam, because of the phase shift which may occur between the former and. the'latter. Such a phase-shift is sometimes diiiicult to compensate. That is why it is sometimes preferred to pick up only the energy yielded by the beam whileY giving up vthe energy existing in the delay line and dissipating this energy in a suitable load. This results in a` decreaseof the tube efficiency and other inconvenielnces.Y A Y AIt isan Iobject of the present invention to eliminate these disadvantages. More speciiically,the invention has for'its object t'o'provide a tube of the type described in the above-mentioned patent, the delay line of which consists of two different sections and in which the whole of the ultra high frequency energy is abstracted from the beam.

The first section of the line, i.e. the section adjacent the cathode, behaves as the delay line of a conventional traveling wave amplifier and is the seat of a traveling wave which is amplified in the usual way by interaction with the beam.

The second section is so dirnensioned that the interaction between tbe wave and the electron beam results in the amplilication of the ultra high frequency energy in the beam wherein the electron bunching is increased, while the ultra high frequency wave, when it reaches the end of the delay line remote from the cathode, is sufciently attenuated to make any dissipation of the ultra high frequency energy in delay line unnecessary.

The invention will be better understood from the following description taken in conjunction with the appended drawing wherein,

Fig. 1 shows in longitudinal section a rst embodiment of the tube according to the invention;

Fig. 2 shows, also in longitudinal section, another embodiment of the invention.

Fig. l shows a tube comprising a vacuum-tight envelope 1. At one end of this envelope is arranged an electron gun 2, of known type, comprising essentially a cathode 21 and an optical system 22 which is grounded. The cathode is biased to negative voltage by a source 23.

The gun 2 directs a cylindrical electron beam through a sequence of cascade-coupled cavity resonators 6 and 7 coaxial with the beam. These resonators are respectively bound by partitions which are transverse with respect 2,922,920 Y, Patented Jan.' 26, 1960 ice,

to the envelope 1. The beam is coupled with these cavities by means of a number of apertures arranged in cylinders 9, coaxial with the envelope and through which the beam is propagated.

Starting from the gun of the tube, a irst plurality of identical resonators 6, four in the embodiment shown, are first encountered. The longitudinal dimension of the remaining cavities 7 is greater than the same dimension of resonators 6. More generally, the longitudinal dimension of resonators 7 increases with their respective distance to electron gun 2. This dimension increases from one resonator to the adjacent one or it increases by steps, several adjacent cavities V7 having the same longitudinal dimension.

An input transmisison line 13v is coupled to the cavity. Y r 6 adjacent gun 2. Each cavity is coupled to the adjacent made up by resonators 6 is concerned, is entirely thatl of a conventional traveling wave amplifier tube. The propagation velocity of the beam is so adjusted that, in

the absence of any wave fed to input 13, it is slightly higher than the phase velocity of the wave propagated along the delay line formed by the cavities 6. The difference between the above two velocities should be of about 10 to 20% of the beam velocity. The wave fed to the tube through input 13 is amplified by interaction with theelectron beam, which loses energy to the wave, while the wave at the same time loses a certain amount of energy to the beam, whereby the latter is.bunched. However, as is well known, the amountof energy gained by the wave from the beam is substantiallyv higher than the amount of energy lost by the wave to the beam. The energy surrendered by the electrons is taken'.

from their kinetic energy. As a result, while the wave is amplified, the electrons are slowed down.

In the second portion of the line, since the longitudinal dimension of the cavities 7 is greater, the phase velocity of the wave increases. The dimensions of the cavities are such that the phase velocity of the wave is by 10 to '20% higher than the beam velocity in the absence of any wave fed to the tube.

Accordingly, the electrons surrender less energy to the wave than the latter surenders to the electrons. In other words, the wave is attenuated while the electrons are accelerated and hunched.

If the line is of sutcient length, the wave is practically extinguished as it reaches the last cavity 10, and there is therefore no need to dissipate this energy in an attenuating load. Substantially the whole of the ultra high frequency energy is in the electron beam when the latter reaches cavity 10 to which it surrenders this energy. This energy s collected by the output 14.

Fig. 2, where the same reference numerals have been used to designate the same elements as in Fig. l, shows another embodiment of the invention.

The delay line is in the form of a helix I15 and an attenuator 18 is provided around the intermediate portion of 3 The operation of the tube of Fig. 2 is the same as the operation of the tube shown in Fig. 1.

What I claim is:

l. A traveling wave amplifier tube comprising an electron gun located at'one end of the tube forv emittingan electron beam, a collector electrode at the other end of thetube for collecting said electrons, a -cavity resonator adjacent to said collector and traversed by said beam, rst and second series-connected delay line portions coupled with said beam along the portions thereof` adjacent said gun and said cavity, respectively, input means near said gun for supplying ultra high frequency wave energy to said first delay line portion, and output means for ex-V tracting ultra high frequency energy from said cavity resonator, said first delay line portion having a delay ratio such that interaction therealong between said wave and .said beam increases the wave energy while the beam is hunched, said second delay line portion having a delay ratio lower than that of said first portion and decreasing toward said collector so that interaction therealong between said wave and said beam decreases the wave energy while the bunching of the beam is further increased and therewith the ultra high frequency energy component thereof is also increased, whereby amplified ultra high frequency is induced in said cavity resonator.

2. A tube as claimed in claim 1, wherein said second portion of said delay line has decreasing delay ratio stepwise in the direction of propagation of the beam.

3. A tube as claimed in claim 2, wherein said delay line comprises a `chain of cascade-coupled cavity resonators, a predetermined number of similarly dimensioned resonators forming said first portion of the delay line whilst resonators forming said second portion of said delay line have their respective longitudinal dimensions increasing in the propagation direction of the beam.

4. A tube as claimed in claim l, wherein said second portion of the delay line has a delay ratio continuously decreasing in the direction of propagation of the beam.

5. Tube as claimed in claim 4, wherein said delay line is a helix having a first constant pitch portion and a second portion with a pitch progresively increasing in the direction of beam propagation.

6. Tube as claimed in claim 5, wherein the output end of said helix is connected to a grounded piece, and further comprising energy absorbing means at an intermediate portion of said helix.

7. A traveling wave tube for amplifying an ultra high frequency energy wave, comprising a delay line, a collector electrode at one end of the delay line, means including a cathodel for directing an electronbeam having a predetermined velocity without ultra high frequency wave energy on said line from said cathode` toward said collector, input means for supplying ultra high frequency wave energy to said delay line, said delay line having first and second portions extending from an intermediate point thereof toward said cathode and collector, respectively, said rst delay line portion having a delay ratio of constant value, said second portion having a delay ratio lower than said tirst portion and decreasing from said intermediate pointl toward the collector, said predetermined electron beam velocity being higher than the wave phase velocity along said first delay line portion and lower than the wave phase velocity along the second portion, said delay ratios and said beam velocity being sorelated that said beam interacts with said wave energyto amplify the same at the rst line portion while along said second portion the amplified wave yields ultra high frequency energy to said beam, and means defining a resonant cavity for receiving energy from the beam, andV out` put means coupled to said cavity for extracting ultra high frequency energy induced therein by said beam. l

References Cited in the tile of this patent UNITED STATES PATENTS 2,284,751 Linder June 2, 1941 2,289,952 Zworykin 'July 14, 19,42 2,463,267 Hahn Mar. l, 1949 2,543,082 Webster Feb. 27, 1951 2,580,007 Dohler et al. Dec. 25, 1951 2,630,544 Tiley Mar. 3, 1953 2,636,948 Pierce Apr. 28, 1953 2,637,001 Pierce Apr. 28, 1953 2,762,948 Field r Sept. 1,1, 195,6 2,794,143 Warnecke et al May 28, 195,7 

